Method of forming articles from a plastic material

ABSTRACT

The molding machine of the present invention comprises a screw extruder for extruding plastic material. A plurality of molds are moved one at a time to the outlet end of the extruder for receiving the plastic material therefrom, One end of the mold is open for receiving the plastic material and the opposite end of the mold includes a closure plate covering the end of the mold. The closure plate has a small fill sensing aperture therein. A sensing switch is mounted adjacent the fill sensing aperture and is adapted to sense when molded plastic exits from the fill sensing aperture so as to shut off the extruder and cause the mold to move away from the extruder so that an additional mold can be filled. A cylinder operated closure device clamps the opposite ends of the mold after the mold has moved away from the filling station so as to contain the plastic material within the mold while the plastic material cools and hardens. A trimming knife trims the ends of the mold as it is moving from its fill station to the clamping station.

This is a division, of application Ser. No. 798,886, filed Nov. 18,1985, now U.S. Pat. No. 4,626,189.

BACKGROUND OF THE INVENTION

This invention relates to a method and machine for forming articles froma plastic material. The present invention is particularly adapted fortaking waste plastic materials of various heterogeneous make-up, andprocessing these materials into products which have properties similarto wood.

One example of a prior process for working up waste plastic material isknown by the name of the "Reverzer" process, introduced by the Japanesecompany Mitsubishi Petrochemical, and mentioned in U.S. Pat. No.4,187,352. According to this process, sorted or unsorted thermoplasticwaste material of, for example, polyethylene, polypropylene,polyvinylchloride or mixtures thereof, is comminuted, and theparticulate material is subsequently stored in a storage space. Theparticulate material is dried to a certain extent, using the heatreleased during the comminution of the waste material. From the storagespace, the particulate waste material is supplied to the "Reverzer"unit, which in essence is a melting unit, comprising a hopper in whichthe material is softened, and a mixer comprising a screw member, inwhich the material is also fluidized. The fluid material is theninjected under very high pressure into a closed mold and thus molded.The molds are then transported to a cooling space, and cooled by beingsprayed with water. The molds are then opened and the molded product isremoved. The resulting products may have the form of tapered beams,frames, U-beams, etc., depending upon the mold being used. In this priorprocess, a very high pressure is built up in the mixing and fluidizationstage of the apparatus used, under the influence of which, as stated,the fluid material is injected into a special pressure resistant mold.

Klobbie U.S. Pat. No. 4,187,352, discloses a method for working upthermoplastic plastic synthetic material into shaped particles in whichspecially adapted pressure resistant apparatus is unnecessary, butcommercially available non-pressure resistant apparatus and dies ormolds can be used.

The Klobbie patent discloses apparatus in which the synthetic materialis subjected to a mixing operation in a housing comprising a screwmember, and is fluidized, molded, cooled in the mold, and removed fromthe mold. The synthetic material is supplied to an extruder without ascreen pack and without an extrusion nozzle. The mold into which it isextruded is open at both ends so that the fluid is not under pressurewithin the mold. Molding pressure is obtained by mixing with theparticulate synthetic material a blowing agent, the threshholdtemperature of which is exceeded at the temperature occurring in theextruder. The blowing agent causes gas to be propogated so as toincrease the pressure within the mold, thereby causing the plasticmaterial to assume the shape of the mold.

Therefore, a primary object of the present invention is the provision ofan improved machine and method for reprocessing waste polymers to createa molded product under low pressure.

A further object of the present invention is the provision of a machineand process which utilizes low pressure so as to permit the use of aninexpensive mold, but at the same time using a pressure which is higherthan that shown in the Klobbie reference referred to above.

A further object of the present invention is the provision of a machinefor molding waste polymers which creates a molding pressure within theextruder by use of a nozzle and a screen pack.

A further object of the present invention is the provision of animproved machine for processing waste polymers wherein the polymers canbe contaminated with various impurities.

A further object of the present invention is the provision of a machinefor processing waste polymers which includes a closure divice forclosing off the ends of the molds during the molding process.

A further object of the present invention is the provision of a machinefor molding waster polymers at a low pressure, but which providessufficient molding pressure without the need of a blowing agent as shownin the Klobbie patent.

A further object of the present invention is the provision of a machinewhich includes an automatic fill sensing device which senses when themold is full and causes it to be indexed away from the extruder.

A further object of the present invention is the provision of a machinefor processing waste polymers which utilizes a heating band to cause thewaste polymers to achieve a fluid state for extruding.

A further object of the present invention is the provision of an machinewhich is economical to manufacture, durable in use and efficient inoperation.

SUMMARY OF THE INVENTION

The present invention provides a machine for forming products out ofwaste polymer materials by utilizing a molding pressure substantiallygreater than that shown in the Klobbie patent referred to above, butsubstantially less than the high pressure molding referred to in the"Reverzer" process referred to above. As a result, the advantages ofmolding with a relatively low pressure, i.e., the inexpensive equipmentand molds, are achieved with the present invention, while at the sametime eliminating the disadvantages encountered with the Klobbie process.

The present invention utilizes an extruder having a screen pack andnozzle head therein. A heater ban surrounds the nozzle so as to supplyheat to the plastic material before it is extruded. The use of thescreen pack an the nozzle create a higher pressure for the plasticmaterial than the pressure obtained in the Klobbie patent. Pressures inthe mold need to be sufficiently high to give good quality moldings. Forsimple moldings, lower pressures give adequate quality, but if the moldhas any detail to be shown, then higher pressures are required.Typically the lowest pressure which would produce acceptable moldingswould be approximately 30 psi and the highest pressure would beapproximately 100 psi. The preferred pressure is dependent upon thenature of the mold.

The plastic materials which may be molded with the present inventioninclude a variety of materials such as low, medium, or high densitypolyethylene; polypropylene; polystyrene; ABS; polyamide; and polyester.The input materials can be mixed and can have low quality with a largenumber of impurities therein.

The present invention utilizes a mold holder which holds a plurality ofmolds and which indexes the molds one at a time, first to a fill stationwhere the molds receive the plastic material from the extruder, and thento a second station wherein the ends of the mold are closed and themolded material is permitted to cool and harden while under pressure.Between the fill station and the second station, a trimming apparatus isprovided for trimming any excess material from the ends of the moldprior to the time that the ends of the mold are closed at the secondstation.

After filling the machine rotates the mold holder to bring an empty moldto the filling station. The mold is filled, and a sensing device at theend of the mold senses when the mold has been filled.

The full mold is taken to a holding station where it is held closed.Closure at the fill orifice is maintained by a pressure piston whichpresses the fill opening of the mold against a flat metal plate. At theefflux orifice at the other end of the mold, closure is maintained bythe pressure piston pressing against the end plate of the mold. Thispiston is held in place by a pneumatic cylinder which also generates thepressure to give closure at the inlet orifice.

After the mold has been filled, the resin that has issued from the moldmust be trimmed flush with the end face of the mold, thus allowing agood seal by the mold closing device. This operation is performed by aself-positioning cutter located between the fill station and the holdingstatin.

The extruder of the present invention utilizes both a screen pack and anextruder nozzle. The screen pack has the function of removingcontamination by impurities which can cause difficulties in the moldfilling operation. These difficulties are chiefly due to the release ofentrained gases when the pressure is reduced at the nozzle.

The nozzle has two functions. It gnerates a pressure in the extruder andinsures complete mixing of the various components of the input material.It also enables the molds to be filled from a relatively small orificeso as to allow such molds to be of relatively small cross-section areawhen compared with the extruder barrel diameter.

Nozzle heater bands are thermostatically controlled so as to hold theextrudant at a fairly constant temperature and so as to give the desiredflow properties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of the present invention showingportions thereof in section.

FIG. 2 is a top plan view of the righthand portion of the device shownin FIG. 1.

FIG. 3 is a sectional view taken along line 3--3 of FIG. 2.

FIG. 4 is a sectional view taken along line 4--4 of FIG. 3.

FIG. 5 is a sectional view taken along line 5--5 of FIG. 3.

FIG. 6 is a sectional view taken along line 6--6 of FIG. 3.

DETAILED DESCRIPTION OF THE PREFEERED EMBODIMENT.

Referring to the drawings, the numeral 10 generally designates themachine of the present invention. Machine 10 includes a screw extrudingmachine 12. Any commercially available extruder for processingpolyethylene will work satisfactorily with the present invention.Extruding machine 12 includes an input hopper 14 for adding thecomminuted plastic waste materials which will be extruded through themachine. Extruder 12 includes an extruding barrel 16 (FIG. 4) having ascrew 18 therein for driving the plastic material toward the dischargeend of the barrel. At the discharge end of the barrel is a nozzle 20having an extrusion aperture 22 therein. A screen pack 24 includes ascreen plate 26 which is mounted for vertical sliding movement in a slot28. Attached to screen plate 26 is a rod 30 which in turn is connectedto a lifting device 32. Lifting device 32 may be a pneumatic cylinderwhich permits the upward lifting of the screen pact out of slot 28 forcleaning periodically. Other means may be used for lifting screen 26.The screen pack as shown in the drawings is fitted between the end ofthe extruder barrel and the nozzle. Other types of screen packs may beutilized than that shown in the drawings, but a self-cleaning type ofpack is preferable. In operation, the screen pack has the function ofremoving contamination or impurities which can cause difficulties in themold filling operation. These difficulties often arise due to therelease of entrained gases when the pressure is reduced at the nozzle.

The nozzle has the function of generating a pressure in the extruder soas to insure complete mixing of the various components of the inputmaterial. Furthermore, the nozzle enables the molds to be filled from arelatively small orifice so as to allow the molds to be of a relativelysmall cross-section area when compared with the extruder barreldiameter.

A nozzle heater band 34 surrounds nozzle 20 and is adapted to permitthermostatic control of the temperature of the extruded material,thereby maintaining the material at a constant temperature to obtain thedesired flow properties at the nozzle head.

The nozzle is bolted or otherwise operatively secured to a largecircular fixed plate 36 which remains stationary with respect to theextruder machine 12. Also attached to the extruding machine 12 is arectangular tank 38 having side walls 40, 42, end walls 44, 46, and abottom wall 48. Tank 38 is adapted to hold a water bath or other coolingfluid 50 therein.

Mounted in the bottom of tank 38 are a pair of upstanding pedestals 52,54 which include bearings 56, 58 at their upper ends for rotatablyreceiving a tubular shaft 60 therein. Shaft 60 extends rotatably inbearings 56, 58 and also extends rotatably through a sleeve 62 centrallylocated in circular plate 36.

Mounted on the outside of shaft 60 are a pair of spaced apart carouselplates 64, 66. Each plate 64, 66 includes a cylindrical sleeve 68 havinga bushing 70 therein. Threaded within sleeves 68 are tightening rods 72which are adapted to tighten against bushings 70 so as to clamp plates64, 66 against sliding movement along shaft 70. The distance betweenplates 64, 66 may be adjusted by loosening rods 72 and by sliding theplates 64, 66 to the desired relative spaced apart positions.

Each plate 64, 66 includes a plurality of circular openings 74 therein.Mounted within openings 74 and spanning the distance between carouselplates 64, 66 are a plurality of elongated molds 76. Each mold includesa first open end 78 and a second closed end 80. Fitted over end 80 is aclosure plate 82 (FIG. 4) having an efflux orifice 83 therein forpermitting gases to escape as the mold is being filled. Closure plate 82is circular and is retentively fitted within the circular opening 74 ofcarousel plate 66. Open end 78 of mold 76 is fitted against circularplate 36. Welded or otherwise secured to the outer surface of mold 76 isa circular plate 84 which is sized to fit retentively within the opening74 of carousel plate 64. Thus molds 76 are suspended between carouselplates 64, 66 by means of closure plate 74 and circular plate 84 beingfitted within the openings 74 of carousel plates 64, 66. The particularmeans for holding circular plates 82, 84 in openings 74 may vary, andmay include clamps, set screws or other means so as to attach the moldsto the carousel plates 64, 66.

Mounted to the end of shaft 60 is a pulley 86. A drive motor 88 includesan output shaft 90 having a pulley 92 thereon. A belt 94 is trainedaround pulley 92 and pulley 86 so as to provide driving connectionbetween motor 88 and shaft 60, thereby providing means for rotating theshaft 60 and the carousel plates 64, 66. A control box 95 is adapted tocontrol motor 88 so as to cause the carousel plates 64, 66 to be movedin increments one at a time which will cause the various molds to moveone at a time from a filling station designated by the numeral 96 inFIG. 3 to a holding or hardening station 98, and thence to periodicother stations 100-110 as shown in FIG. 3.

Mounted for sliding movement on the upper edges of side walls 40, 42 oftank 38 is a sliding frame 112 having a pair of cross frame members 114spanning the distance between side walls 40, 42. Fixed to cross framemembers 114 is a fill sensing assembly 116 which includes a fill sensingbox 118 positioned in facing relationship to carousel plate 66 at thefill station 96. Fill sensing box 118 is shown in section in FIG. 4 andincludes an elongated arm or blade 120 which is pivoted at 122. On thelower end of arm 120 is a balance weight 124 which fits in facingrelationship to aperture 83 in closure plate 82 of mold 76. The upperend of arm 120 is provided with a magnet 126 which is normally inengagement with a magnet reed switch 128. In this normal position,magnetic reed switch 128 controls motor 88 so that there is norotational movement of the carousel plates when the mold 76 is at thefill station 96.

Upon actuation of the screw extruding machine, plastic material isextruded outwardly through extrusion aperture 22 into mold 76. As theplastic material begins filling the mold 76, it ultimately beginsissuing outwardly through fill sensing aperture 83. when this happens,couter balance 124 is moved to the right as viewed in FIG. 4, therebycausing magnet 126 to break contact with magnetic reed switch 128. Whencontact is broken between magnet 126 and magnetic reed switch 128, theextruder is stopped and motor 88 causes the carousel plates 64, 66 to beindexed and moved so that the mold 76 progresses from the fill station96 to the hardening station 98.

Positioned between fill station 96 and hardening station 98 is a spruecutting device 130 shown in FIGS. 2, 3 and 5. Sprue cutting device 130includes a base frame 132 which is fixed to sliding frame 12 and whichextends downwardly therefrom. At the lower end of base frame 132 ispivoted a knife arm 134 having a knife blade 136 thereon. A hydraulic orpneumatic cylinder 138 is connected at one of its ends to base frame 132and at the other of its ends to knife arm 134. Cylinder 138 maintainsknife blade 136 in facing relationship to the outer surface of closureplate 82, and is adapted to trim any resin that has issued from theorifice 83 of the mold. As the mold moves from the fill stations 96 tothe hardening station 98, the blade 136 wipes along the surface ofclosure plate 82 and trims the mold flush with the end face.

Mounted at the hardening station 98 is a mold closing device 140. Device140 includes a cylinder 142 which is rigidly mounted with respect tosliding frame 112. Cylinder 142 includes a rod 144 having at its outerend a circular pad 146 adapted to fit in sealing engagement over fillsensing aperture 83. When the mold 76 reaches the hardening station 98it stops, and cylinder 142 is extended so that pad 146 fits in sealingengagement over aperture 83. The pad 146 also exerts axial pressure onmold 76 so as to cause the open end 78 to mold 76 to be tightly fittedagainst the surface of fixed plate 36. Thus, both ends of mold 76 areclosed by virtue of the pneumatic cylinder 142 during the time that themold is at hardening station 98.

At the same time, the mold immediately following mold 76 is now at thefill station and is being filled. With the next indexing of the carouselplates, the second mold comes to the hardening station and the firstmold progresses downwardly toward the bath 50 within tank 38. By thistime the plastic material has hardened within mold 76 and does notrequire closure at the opposite ends of the mold 76.

After the molds have been more thoroughly cooled by subjecting them tothe cooling bath 50, they can be emptied and used again for the formingof additional products.

The present invention thus permits the molds to be filled at arelatively low pressure, so as to elminate the need for more expensivemolds used in the high pressure molding techniques. However, the presentinvention permits the molds to be filled under somewhat greater pressurethan that achieved with the Klobbie patent discussed above. There istherefore no need for a blowing agent to provide the molding pressurewithin the mold. The fill sensing device provides an improved method fordetermining when the mold is full and automatically signaling themachine to index the mold to the next station. The trimming blade andapparatus 130 trims the end of the mold automatically so as to insure atight seal when the mold is positioned in the hardening station. At thehardening station, the mold is closed at both ends so as to permit themolded material to completely harden with both ends of the mold closed.

Thus, it can be seen that the device accomplishes at least all of itsstated objectives.

What is claimed is:
 1. A method of molding articles from a plasticmaterial comprising:introducing said plastic material into an extruderapparatus; heating and mixing said plastic material to be in a fluidcondition; maintaining said fluid plastic material free from a blowingagent; introducing said fluid plastic material from said extruderapparatus into a first end of a mold, said mold having an opposite endwith a closure plate thereover, said closure plate having an aperturetherein; said mold being mounted on a mold-holding frame holding aplurality of additional elongated molds; using a nozzle of said extruderapparatus to increase pressure in said extruder; sensing when said moldhad been filled by automatically sensing the issuance of said plasticfluid from said aperture; moving said mold-holding frame as to causesaid mold to move to a second station in response to sensing theissuance of plastic fluid from said aperture; simultaneously moving oneof said additional molds into fluid communication with said extruderapparatus;closing both of said first and second ends while said mold isat said second station so that said fluid plastic can cool and harden;introducing fluid plastic material into said one additional mold at thesame time that said mold is at said second station.
 2. A methodaccording to claim 1 and further comprising using trimming means toengage and trim the excess portions of said plastic material which haveissued from said aperture of said closure plate, said trimming beingflush with said closure plate and being accomplished during the timethat said mold is moving to said second station.
 3. A method accordingto claim 1 and further comprising screening said plastic material withinsaid extruder apparatus before said plastic material is introduced intosaid mold.
 4. A method according to claim 3 and further comprising usinga heater band surrounding said nozzle of said extruder apparatus toapply heat to said plastic material.
 5. A method according to claim 1,further comprising issuing said plastic fluid through said aperture andsensing when said plastic fluid has filled said aperture.